Intermittent Alarms at HMI Start Up?

[Twitch 1]

Hi,

I am using Factory Talk View ME v8.1 with RS Studio 5000 v24 on a 1769-L33ER controller.

I have a project that exhibits some strange behavior. With the PLC up and running normally I now fire up the HMI and it will sometimes immediately trigger an alarm. The alarm message is configured to display the failing measured numeric and the test limit values being used, and so it is obvious that there is bogus data (large negative numbers) in those tag values when the alarm triggers.  But when I watch the tags in RS Studio I can see that they are stable and correct where used in the scaling math during the HMI boot.  Once the HMI is active they behave properly as can be proven through alarm testing.  It seems that there are transient values being used as the HMI boots up?

Through the history of this HMI development I've seen the problem move to a different alarm, disappear, reappear on a different alarm, and now disappear again as new HMI builds are generated.

Can anyone explain what might be happening or especially suggest how to prevent it?

Tim

[AndrewG 13]

Here is what I would try:

-Make a list of all the alarms that are being incorrectly triggered

-Figure out where each alarm is triggered in the PLC

-Add some timers in the PLC to put a time delay on these alarms. For example: let's say when Tag1 is High, Alarm 1 is triggered. Add a timer so that when Tag1 is High for 10 seconds, Alarm 1 is triggered. Depending on your system this may or may not be a good solution but I do this a lot with alarms.

[kaiser_will 65]

When your process demonstrates "bogus" alarm events during startup, a startup inhibit process may need to be added to suppress all alarm events for a brief period during HMI startup.  

You could...create a new PLC tag (HMI_Startup); add a HMI startup macro to energize HMI_Startup (this tag will only be ON at HMI power-up via the macro execution); add PLC code one-shot to seal in a startup timer (30 sec) and latch off HMI_Startup; add PLC code to energize new tag HMI_Startup_Disable that is energized when startup timer is timing; add normally-open HMI_Startup_Disable tag to every alarm event to suppress the alarm during startup.

http://www.plctalk.net/qanda/archive/index.php/t-80134.html

[Twitch 1]

"...create a new PLC tag (HMI_Startup); add a HMI startup macro to energize HMI_Startup "

Thanks kaiser_will, I think this is a terrific idea and will give it a try!

 

AndrewG: thanks for helping.  Your idea would definitely work for some types of alarms but some I'm having trouble with are 'over-current' sensors, and for these I would like to alarm ASAP as to save hardware from damage.